For lithographic fine patterning in semiconductor manufacturing processes, there has been a demand for resist compositions that can be exposed at shorter wavelengths and show a wide depth of focus tolerance (abbreviated as “DOF”), a small line edge roughness (abbreviated as “LED”), high resolution, high sensitivity, good substrate adhesion and good etching resistance.
“Chemically amplified resist compositions” have been used for the reduction of the exposure wavelength. The chemically amplified resist composition is a pattern forming material that contains an acid generator (called “photoacid generator”) capable of generating an acid by exposure and forms a pattern by changing the structure of the resist resin by the action of the acid generated from the acid generator as a catalyst and thereby causing a difference in developer solubility between exposed and unexposed portions of the resist film.
As photoacid generators of chemically amplified resist composition for exposure at 248 nm wavelength (KrF laser radiation), there are generally used those capable generating perfluoroalkanesulfonic acids of long chain and high acidity. However, the perfluorooctanesulfonic acid and derivatives thereof (PFOS) have the problems concerning the stability (non-degradability) due to C—F bonds and the biological concentration and accumulation due to hydrophobic and lipophilic natures. The same problems are also being raised against the perfluoroalkanesulfonic acids of 5 or more carbon atoms and their derivatives. For such a reason, the U.S. Environmental Protection Agency has proposed a rule to regulate the use of these compounds.
Under the above circumstances, alkoxycarbonylfluoroalkanesulfonic acid onium salts such triphenylsulfonium methoxycarbonyldifluoromethanesulfonate (Patent Document 1), (4-methylphenyl)diphenylsulfonyl t-butoxycarbonyldifluoromethanesulfonate (Patent Document 2) and triphenylsulfonium (adamantane-1-ylmethyl)oxycarbonyldifluoromethanesulfonate (Patent Document 3) have been developed as acid generators, each of which is capable of generating a partially- or fully-fluorinated, lower-carbon-number alkanesulfonic acid of sufficient acidity and less environmental load.
However, the alkoxycarbonylfluoroalkanesulfonic acid onium salts developed as the photoacid generators have significantly low solubility in ordinary resist solvents (such as propylene glycol monomethylether acetate). There thus remains a problem that it is difficult to introduce a large amount of such onium salt acid generators in the resist compositions so that the resist compositions cannot exhibit adequate performance (DOF, LER, resolution etc.).